Born in Taranaki in 1892 to William James Mathieson and Mary Ann Hunt (or Howaiki), and known as Bert. Some sources give his full name as Thomas Berge Tupkea Mathieson. His name Berge seems to have come from his grandfather Thomas Burge Mathieson: both Berge/Burge and Matheson/Mathieson were spelt inconsistently in family and official records.
When he joined up just before Christmas in 1916 Bert was working as a motor mechanic in New Plymouth. After training in New Zealand he sailed for England in mid-1917 with the 26th Reinforcements and within a few months found himself on the Western Front as a driver delivering ammunition to the New Zealand Field Artillery.
His time on the front line came to an end in July 1918 when he was admitted to a military hospital in France with a hernia — a condition he declared when joining up and which had earlier caused him to be rejected for military service. Once recovered he spent a few months behind the lines at base depot before being reclassified as unfit for service and sent back to England. He left on a troopship for New Zealand just before Christmas in 1918.
In 1919 Bert married Norah Laura Te Aroaro o Paritutu Ruakere and they had a family of seven. One son, Rex Tawheta Mathieson, was killed in action in the Pacific during World War 2 when his aircraft was shot down. Bert died in Taranaki in 1961.